Quantum Signatures of Cosmic Topology: How Casimir Backreaction Transmits Isotropy Violation

TL;DR

This paper demonstrates that quantum effects from non-trivial cosmic topology, specifically Casimir energy, can induce anisotropic expansion in the universe, challenging the assumption of initial isotropy.

Contribution

It provides a detailed calculation of the Casimir stress-energy tensor for scalar fields and shows its backreaction causes anisotropy during de Sitter expansion.

Findings

Casimir energy contributes to stress-energy tensor in universes with non-trivial topology.

Quantum backreaction can induce anisotropic expansion from initially isotropic states.

Topological quantum effects leave imprints that break local homogeneity and isotropy.

Abstract

A finite, scheme-independent Casimir contribution to the stress-energy tensor arises naturally for quantum fields in universes with non-trivial spatial topology. We compute this Casimir stress-energy tensor contribution for a conformally coupled scalar field and for a minimally coupled scalar field. We show that, for the conformally coupled case, the backreaction of this contribution to the Einstein equations during an expanding de Sitter phase drives anisotropic expansion even when the Universe begins in a locally homogeneous and isotropic state. We conclude that quantum imprints of the underlying non-trivial topology inevitably give rise to local departures from homogeneity and isotropy.